ABSTRACT: While others have examined the implementation and/or the stringency of enforcement of antitrust laws in post-socialist economies, this paper is the first study that attempts to explain the determinants of antitrust enforcement activity across post-socialist countries using economic and political variables. Using a panel of ten European post-socialist countries over periods ranging from 4 to 11 years, we find a number of significant determinants of enforcement in these countries. For example, larger economies engage in more antitrust enforcement, and countries have tended to increase their enforcement efforts over time. Our results also suggest that countries characterized by more unionization and less corruption tend to engage in greater antitrust enforcement of all types. Countries more successful in privatizing have filed fewer cases, while more affluent or developed countries investigate fewer cases of all types, cons! istent with an income-shifting motivation for antitrust.